This invention relates to the field of optical scanners. More specifically, the invention relates to an optical scanner, such as a bar code scanner, which can operate in extreme thermal conditions without performance degradation due to condensation and frost.
Electro-optical scanners, such as bar code symbol scanners, are now quite common. Typically, a bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e., the bars, and/or the widths of the light regions, i.e., the spaces between the bars, when partitioned into groups, indicate encoded information to be read.
A bar code symbol reader illuminates the symbol and senses light reflected from the coded regions to detect the widths and spacings of the coded regions and derive the encoded information. Bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example to provide efficient inventories, tracking of work in progress, etc.
A variety of scanning systems are known. One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components of the type exemplified by U.S. Pat. Nos. 4,387,297 and 4,760,248xe2x80x94which are owned by the assignee of the instant invention and are incorporated by reference hereinxe2x80x94have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a hand-held or stationary scanner.
FIG. 1 illustrates an example of a prior art bar code symbol reader 10 implemented as a gun shaped device, having a pistol-grip type of handle 53. A lightweight plastic housing 55 contains a light source 46, a detector 58, optics 57, signal processing circuitry 63, a programmed microprocessor 40, and a power source or battery 62. An exit window 56 at the front end of the housing 55 allows an outgoing light beam 51 to exit and an incoming reflected light 52 to enter. A user aims the reader at a bar code symbol 70 from a position in which the reader 10 is spaced from the symbol, i.e. not touching the symbol or moving across the symbol.
As further depicted in FIG. 1, the optics may include a suitable lens 57 (or multiple lens system) to focus the scanned beam into a scanning spot at an appropriate reference plane. The light source 46, such as a semiconductor laser diode, introduces a light beam into an optical axis of the lens 57, and other lenses or beam shaping structures as needed. The beam is reflected from an oscillating mirror 59 which is coupled to a scanning drive motor 60 energized when a trigger 54 is manually pulled. The oscillation of the mirror 59 causes the outgoing beam 51 to scan back and forth in a desired pattern.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297 and 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multi-mirror construction is mounted.
The light 52 reflected back by the symbol 70 passes back through the window 56 for transmission to the detector 58. In the exemplary reader shown in FIG. 1, the reflected light reflects off a mirror 59, passes through an optical filter 47 and impinges on the light sensitive detector 58. The filter is typically designed to have a band-pass characteristic in order to pass the reflected (return) laser light and block the light coming from other optical sources. The detector 58 produces an analog signal proportional to the intensity of the reflected light 52.
The signal processing circuitry includes a digitizer 63 mounted on a printed circuit board 61. The digitizer processes the analog signal from detector 58 to produce a pulse signal where the widths and spacings between the pulses correspond to the widths of the bars and the spacings between the bars. The digitizer serves as an edge detector or wave shaper circuit, and a threshold value set by the digitizer determines what points of the analog signal represent bar edges. The pulse signal from the digitizer 63 is applied to a decoder, typically incorporated in the programmed microprocessor 40 which will also have associated program memory and random access data memory. The microprocessor decoder 40 first determines the pulse widths and spacings of the signal from the digitizer. The decoder then analyses the widths and spacings to find and decode a legitimate bar code message. This includes analysis to recognize legitimate characters and sequences, as defined by the appropriate code standard. This may also include an initial recognition of the particular standard to which the scanned symbol conforms. This recognition of the standard is typically referred to as autodiscrimination.
To scan the symbol 70, the user aims the bar code reader 10 and operates movable trigger switch 54 to activate the light source 46, the scanning motor 60 and the signal processing circuitry. If the scanning light beam 51 is visible, the operator can see a scan pattern on the surface on which the symbol appears and adjust aiming of the reader 10 accordingly. If the light beam 51 produced by the source 46 is marginally visible, an aiming light may be included. The aiming light, if needed produces a visible-light spot which may be fixed, or scanned just like the laser beam 51. The user employs this visible light to aim the reader at the symbol before pulling the trigger.
The reader 10 may also function as a portable data collection terminal. If so, the reader would include a keyboard 48 and a display 49, such as described in the previously noted U.S. Pat. No. 4,409,470.
In electro-optical scanners (readers) of the type discussed above, the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry can all be packaged in a xe2x80x9cscanning modulexe2x80x9d, which in turn is placed into the scanner""s, or terminal""s housing.
Another type of an optical scanner is a solid state imaging (SSI) reader. The SSI reader will typically contain a solid state detector, such as a charge coupled device (CCD) or a metal-oxide semiconductor field effect transistor (MOSFET). Imaging scanners do not use a moving spot to illuminate an indicia being read, but instead flood illuminate the target, or use flood illumination from external sources, and detect the reflected light from at least a portion of the illuminated target.
Both, the scanning-type readers and the SSI-type readers have found wide acceptance in the retail, wholesale and industrial applications, such as point-of-sale, warehouse and manufacturing operations. Bar code readers are typically specified to operate in non-condensing environments. Certain applications require the reader to operate over a wide temperature range, for example from xe2x88x9230 to 50 degrees Celsius. In certain situations, such as when an operator must use the scanner inside and outside of a freezer, moving the scanner back and forth between hot to cold locations creates condensing environment around and inside the scanner. Condensation can form on both, exterior and interior surfaces of the scanner. The reader""s exit window is particularly susceptible to condensation and frost. External condensation on the exit window can disable scanning by altering the outgoing scan beam. Internal condensation on the optical elements can do the same, and the condensation on the electronic components can cause short circuits and catastrophic failure of the device. Thus, the result of operating a scanner in a condensing environment can vary from a non-read or a miss-read of a scanned item, to a damaged device.
The need exists for a scanning system which can be operated in a condensing environment.
The need also exists for a scanning system which can be operated in cold and hot environments without degradation in performance due to frost and condensation.
The need also exits for an indicia reader which is not susceptible to condensation and frost, and allows for an uninterrupted operation during movements between the hot and cold environments.
The need also exists for a bar code reader which is not susceptible to condensation and frost, and allows an uninterrupted operation during movements between the hot and cold environments.
The need also exists for a laser-type bar code reader which is not susceptible to condensation and frost, and allows an uninterrupted operation during movements between the hot and cold environments.
The need also exists for a SSI type reader which is not susceptible to condensation and frost, and allows an uninterrupted operation during movements between the hot and cold environments.
The present invention is directed to an optical scanner which is not susceptible to condensation and frost and can be moved from hot and cold environments without any down time.
In one preferred embodiment, the applicants invented a heater module which is used to keep the scanner""s internal ambient temperature within a set range. As the scanner is moved from hot to cold environments and the scanner""s internal ambient temperature starts to fall, the heating element inside the heater module gets turned on. A re-circulating fan, also located inside the heater module, forces the air inside the scanner to flow over the heating element. The heated air is blown over the scanner""s internal components, warming them up and preventing condensation. As the temperature of the scanner""s exit window is raised, the likelihood of frost forming on the exterior is also reduced.
In another embodiment, the scanning components are placed in a hermetically sealed enclosure filled with inert gas. The absence of moisture in the enclosure eliminates the problem of condensation on the internal components.